After the release of WordPress 3.9, expect that there are a few problems in your site. If you look at the forums section, you’ll see a lot of complaints, bugs, and errors pertaining to WordPress 3.9 so here are some common issues:
Visual Editor is broken or just disappeared after update.
Issues with plugins and themes. Here is the master list of the known issues in WordPress 3.9.
Add borders or padding to images removed.
When asking for support, be patient, you are not the only one that has this kind of problem especially when requesting for support in forums. And if the volunteer was able to solve your problem, don’t forget to say thanks.
Read the rest of the post here: http://wptavern.com/common-issues-and-troubleshooting-wordpress-3-9